Nanoscopic analysis of oxygen segregation at tilt boundaries in silicon ingots using atom probe tomography combined with TEM and ab initio calculations.

We have developed an analytical method to determine the segregation levels on the same tilt boundaries (TBs) at the same nanoscopic location by a joint use of atom probe tomography and scanning transmission electron microscopy, and discussed the mechanism of oxygen segregation at TBs in silicon ingots in terms of bond distortions around the TBs. The three-dimensional distribution of oxygen atoms was determined at the typical small- and large-angle TBs by atom probe tomography with a low impurity detection limit (0.01 at.% on a TB plane) simultaneously with high spatial resolution (about 0.4 nm). The three-dimensional distribution was correlated with the atomic stress around the TBs; the stress at large-angle TBs was estimated by ab initio calculations based on atomic resolution scanning transmission electron microscopy data and that at small-angle TBs were calculated with the elastic theory based on dark-field transmission electron microscopy data. Oxygen atoms would segregate at bond-centred sites under tensile stress above about 2 GPa, so as to attain a more stable bonding network by reducing the local stress. The number of oxygen atoms segregating in a unit TB area NGB (in atoms nm-2 ) was determined to be proportional to both the number of the atomic sites under tensile stress in a unit TB area nbc and the average concentration of oxygen atoms around the TB [Oi ] (in at.%) with NGB ∼ 50 nbc [Oi ].

Long pulse production of high current D(-) ion beams in the JT-60 negative ion source.

The first long pulse production of high power D(-) ion beams has been demonstrated in the JT-60 U negative ion sources, each of which was designed to produce 22 A, 500 keV D(-) ion beams. Voltage holding capability and the grid power loading were examined for long pulse production of high power D(-) ion beams. From the correlation between voltage holding and the light intensity of cathodoluminescence from the Fiber Reinforced Plastic insulators, the acceleration voltage for stable voltage holding capability was found to be less than 320-340 kV where the light was sufficiently suppressed. By tuning the extraction voltage, the grid power loadings in the ion sources were decreased to the allowable levels for long pulse injection without a significant reduction of the beam power. After tuning the acceleration and extraction voltages, D(-) ion beams of 12.5 and 9.8 A were produced at 340 keV with cesium seeding at a rate of approximately 14 microg/s into the ion sources. The pulse duration of these D(-) ion beams was extended step by step, and then was successfully extended up to 18 s without degradation of the negative ion production. The D(-) ion beams were neutralized to yield 3.6 MW D(0) beams by a gas cell, and then injected into the JT-60 U plasma. Further, a slight reduction of D(-) ion beam power allowed the longer injection duration of 21 s at a D(0) beam power of 3.2 MW. The success in the long pulse production of a high power D(-) ion beam shows that negative ion beams can be produced during a few tens of seconds without degradations of negative ion production and the voltage holding in a large Cs-seeded negative ion source.

Thickness of Retinal Nerve Fiber Layer Decreases after Vitreous Surgery for Idiopathic Macular Hole.

Purpose: The alteration of the retinal nerve fiber thickness (NFLT) before and after vitreous surgery for a macular hole in cases with or without visual field defects was investigated.Methods: The NFLT of 23 eyes with idiopathic macular hole was measured with scanning laser polarimeter up to 12 months after surgery. The NFLT was divided into superior, inferior, nasal, and temporal quadrants. The mean NFLT of each quadrant was analyzed statistically and compared to the results of visual field tests.Results: In all cases, the NFLT decreased significantly up to 3 months after surgery, but increased gradually up to 12 months. In cases with visual field loss, the thickness of the nerve fiber layer that corresponds to the visual field defect diminished strongly, in contrast with other quadrants. Even in cases without visual field loss, the NFLT decreased significantly a month after surgery, especially in the nasal and inferior quadrants.Conclusion: This study demonstrates that the thickness of retinal nerve fiber layer decreases at least one month after surgery, even in cases without visual field defect. This may suggest the existence of a subclinical complication of vitreous surgery.

[Thickness of retinal nerve fiber layer decreases after vitreous surgery for idiopathic macular hole].

PURPOSE: To investigate the alteration of the retinal nerve fiber thickness (NFLT) before and after vitreous surgery for a macular hole in cases with or without visual field defects. METHODS: The NFLT of 23 eyes with idiopathic macular hole was measured with scanning laser polarimeter upto 12 months after surgery. The NFLT was divided into superior, inferior, nasal, and temporal quadrants. The mean NFLT of each quadrant was analyzed statistically and compared to the results of visual field tests. RESULTS: In all cases, the NFLT decreased significantly upto 3 months after surgery, but increased gradually upto 12 months. In cases with visual field loss, the thickness of the nerve fiber layer that corresponds to the visual field defect diminished strongly, in contrast with other quadrants. Even in cases without visual field loss, the NFLT decreased significantly a month after surgery, especially in the nasal and inferior quadrants. CONCLUSION: This study demonstrates that the thickness of retinal nerve fiber layer decreases at least one month after surgery, even in cases without visual field defect. This fact may suggest the existence of a subclinical complication of vitreous surgery.

[Correlation of pathological features of surgically excised choroidal neovascular membranes with age-related macular degeneration and indocyanine green videoangiographic findings].

We surgically excised subfoveal neovascular membranes from eight patients with age-related macular degeneration. The correlation of the histopathological features of choroidal neovascularization and preoperative indocyanine green (ICG) videoangiographic findings were studied. Neovascular membranes which demonstrated hyperfluorescence at an early phase of ICG videoangiography had many vascular channels and a large lumen without enclosure of retinal pigment epithelium (RPE). Fibrovascular tissues contained small vessels with fibrotic stroma that showed hyperfluorescence only at a late phase of ICG videoangiography. In contrast, the membrane which showed hypofluorescence of ICG videoangiography was composed of paucivascular fibrotic tissue covered extensively with RPE. Moreover, newly formed vessels with proliferative endothelium could be observed in the neovascular membranes that showed weak fluorescence or hypofluorescence. These results could provide a morphological basis for the interpretation of ICG videoangiographic features of choroidal neovascularization. It also may be useful in planning the treatment for subfoveal neovascular membranes.